In a cellular system, the geographic area which is serviced by the system is divided into cells. In each cell there is a base station possessing a number of transmitters and receivers, each of which is tuned to a different frequency or radio channel. A mobile subscriber within a cellular system has a transceiver which uses two radio channels to initiate a telephone call. Since government authorities allocate a fixed number of channels for mobile telephonic communications, subdividing the geographic area serviced by a system, or service area, into cells allows the same radio channel to be reused in more than one cell within the service area. Thus, the number of calls which the system can process at any given time is increased. A mobile switching center (MSC) within the service area determines the radio channels to which the mobile subscriber transceiver may tune to communicate with a base station. Furthermore, the MSC switches a base station transceiver to a switched telecommunications network, such as the public switched telephone network (PSTN) for transmission elsewhere.
To obtain mobile telephone service, a mobile subscriber must first make arrangements with a provider of mobile telecommunications services. In most cases, the services offered by the provider will extend beyond the area covered by a single mobile telecommunications system. Typically, the service provider may do so by owning or controlling a network of such mobile telecommunications systems, making arrangements with systems owned by others in other territories, or both. The service provider assigns each mobile telephone subscriber to a home MSC. The home MSC maintains a register called a home location register (HLR) in which subscribers assigned to that MSC are recorded or stored.
FIG. 1 illustrates an example of a network of cellular telecommunications systems. Mobile telecommunications network 100 includes a plurality of MSCs, such as MSC 101, MSC 103 and MSC 104. MSC 103 performs switching operations for base stations 108, 109 and 110 through communication links 113, 114 and 115, respectively. As defined herein, a communication link refers to any medium for transmitting a message. The message may be data, voice and/or video information, in an analog or a digital format. Communication links also include, without limitation, wireline media such as copper or fiberoptic cable, and wireless media such as radio frequency and microwave transmission systems. Similarly, MSC 104 performs the switching operations for base stations 111 and 112 through communication links 116 and 117, respectively. Although not illustrated in FIG. 1, MSC 101 is able to perform switching operations for a plurality of base stations. Each of the plurality of MSCs may be connected to PSTN 102. However, only the connection between MSC 101 and PSTN 102 has been illustrated in FIG. 1.
A mobile subscriber 120, is assigned, or homed, to MSC 101. However, in the example illustrated in FIG. 1, mobile subscriber 120 is travelling between the service areas corresponding to MSC 103 and 104. MSCs 101, 103 and 104 are interconnected by a data network which is represented using communications links 105, 106 and 107. It should be noted that no particular type of network protocol or network topology is intended to be represented by communications links 105, 106 and 107. Communications links 105, 106, and 107 are provided to indicate that each MSC is able to communicate data to another MSC using some form of data communication. Additionally, it should be noted that communications links 105-107 may be included as a portion of the PSTN or as dedicated connections. Furthermore, communications links 105, 106 and 107 are not intended to represent a network for carrying calls, although data may be communicated over the same networks which service voice calls.
During a communications operation, a service provider maintains a service profile for each of its mobile subscribers. A service profile includes information about the services to which a mobile user has subscribed, as well as other data necessary to provide a desired service. For example, a service profile may include information regarding one or more of the following: call forwarding, call waiting, three-way conferencing, calling features indicator, origination indicator, digits restriction, termination restriction code, digits carrier, routing digits, geographic authorization, authentication capability, DMH Account Code digits, DMH alternate billing digits, DMH billing digits, mobile directory number, message waiting notification count, message waiting notification type, origination triggers, PACA indicator, preferred language indicator, SMS origination restriction, SPNI PIN, SPNI Triggers, SMS termination restrictions, termination triggers, and the like.
A service profile for a mobile subscriber is stored by the HLR of the mobile subscriber's home MSC. HLR 121 represents a HLR for mobile subscribers assigned, or homed, to MSC 101. A HLR is implemented by a data processing system associated with a corresponding MSC. Furthermore, it should be noted that while HLR 121 is illustrated separately from MSC 101, this separation does not imply HLR 121 is physically separate from MSC 101. Indeed, the functions of HLR 121 may be performed by a computer which also operates MSC 101. In any instance, an HLR maintains and, as will be subsequently described, distributes to other MSCs, service profiles for subscribers assigned to it and homed to its corresponding MSC.
When a subscriber travels from an area serviced by its home MSC to another service area in the network of the service provider, the visited system will obtain the service profile of the mobile subscriber before providing service to the mobile subscriber. For example, when mobile subscriber 120 moves from a cell of MSC 103 to a cell of MSC 104, mobile subscriber 120 must register for service with MSC 104 before telephone service is available. Such a registration process begins when mobile subscriber 120 sends a standard message to a closest base station corresponding to MSC 104. FIGS. 2, 3 and 4 illustrate a prior art method for transferring service for a mobile subscriber from one visited system to another visited system within network 100. This prior art method is implemented in accordance with the IS41 North American Wireless Standard.
FIG. 2 depicts a flow chart which illustrates the steps performed by HLR 121 of MSC 101 during such a service transfer from a visited MSC 103 to another MSC 104. In step 201, HLR 121 receives a registration notification message from MSC 104. In step 202, the HLR 121 responds to the registration notification message by transmitting a service profile associated with mobile subscriber 120 to MSC 104. MSC 104 stores the service profile within an associated visiting location register (VLR) 123. VLR 123 includes a list of all mobile subscribers visiting the area serviced by MSC 104 and currently registered with MSC 104 for service. VLR 123 of MSC 104, like HLR 121 of MSC 101, is maintained by a data processing system. This data processing system can be part of, or separate from, the MSCs, within a system and may perform additional functions not specifically set forth herein. In the description provided herein, both the register and the data processing system maintaining the register are referred to herein as the VLR.
At step 203, HLR 121 of MSC 101 sends a registration cancel message to MSC 103 to cancel the registration of mobile subscriber 120 within VLR 125 of MSC 103. Thereafter, in step 204, HLR 121 of MSC 101 receives an acknowledgement of the registration cancel message from MSC 103.
FIG. 3 depicts a flow chart illustrating steps performed by VLR 125 of MSC 103. MSC 103 receives the registration cancel message from HLR 121 of MSC 101 in a step 301. In step 302, MSC 103 transmits an acknowledgement of the registration cancel message to HLR 121 of MSC 101. MSC 103 then deletes the service profile associated with mobile subscriber 120 from VLR 125 in step 303.
FIG. 4 illustrates a flow chart indicating a method performed using VLR 123 of MSC 104 to transfer the service of mobile subscriber 120 from MSC 103 to MSC 104. In step 401, MSC 104 (the visited MSC) receives the registration message from mobile subscriber 120. At step 402, MSC 104 transmits the registration notification message to HLR 121 of MSC 101. In step 403, MSC 104 receives the service profile associated with mobile subscriber 120 sent from HLR 121 of MSC 101. This step corresponds to step 202 of FIG. 2. The service profile is subsequently stored within VLR 123 of MSC 104.
The communication of messages and service profiles between MSCs 101, 103 and 104 occur over a data network. represented by communications links 105, 106 and 107.
The methods represented by FIG'S 2, 3 and 4 are partially accomplished through the use of a data processing system implemented at each MSC. An example of such a data processing system is data processing system 500 illustrated in FIG. 5. Data processing system 500 includes a central processing unit (CPU) 510, such as a conventional microprocessor, and a number of other elements interconnected via one or more system buses, which are collectively represented by bus 512. These elements include a random access memory (RAM) 514 for temporary storage of data and program instructions, read only memory (ROM) 516 for read only storage of data and program instructions, an input/output (I/O) adapter 518 for connecting peripheral devices such as disk units 520 and tape drives 540 to bus 512, a user interface adapter 522 for connecting keyboard 524 and mouse 526, a communications adapter 534 for connecting the data processing system to a data network, and a display adapter 536 for connecting bus 512 to display device 538. The data processing system 500 is provided as one embodiment of a data processing system. It should be noted that a data processing system used by a MSC need not include all of the elements illustrated in FIG. 2 and may perform other data processing functions associated with the MSC and not specifically described herein.